Athletic javelin with maximum moment of inertia

ABSTRACT

A competition javelin made to conform to all the rules of the governing body, having the highest possible transverse moment of inertia at its center of gravity. With this dramatic increase in its transverse moment of inertia, the novel javelin&#39;s position in flight is less influenced by the aerodynamic pitching moment, resulting in longer flights.

BACKGROUND OF THE INVENTION

The present invention relates to athletic competition javelins, in particular, a new athletic competition javelin with a maximum transverse moment of inertia.

The javelin is old. With the javelin the cave man went out to get his dinner and over thousands of years the javelin saw battles in many lands. The javelin had purpose and a part in our evolution. Today we celebrate the javelin as a competition in our sports festivals. It is the “event of purpose”, with the objective being to throw the javelin the greatest possible distance.

The construction of the javelin has evolved with the times and available materials. First javelins were relatively straight sticks with sharp points, sometimes with a sharp stone tied to the front, several thousand years later to be replaced by metal. The competition javelins started as wood, with a metal tip and a cord grip in the midsection. When technology made it possible, sports javelins were made out of metal tubing, almost always steel or aluminum, with a metal point in front and a cord grip over the center of gravity. The art was to make an implement, which was light enough and yet not bend or break when thrown. The mass of the javelin was evenly distributed over its full length, except for the front point, which had extra weight to make the javelin stable in flight and land point first. Under these circumstances the javelin's transverse moment of inertia was determined by the current materials used, and was never considered as a factor in flight performance.

However, it was observed that all javelins of the same weight and same length did not fly the same distance, but in fact achieved remarkably different flights. Javelins were constructed to be within the loose rules of the day, without much thought given to experimenting for efficiency of flight, until brothers Franklin and Richard Held started to work seriously to make a better javelin for Franklin Held to throw. They had success and Franklin Held set a world record with one of their home made javelins, which Richard Held started to manufacture. Richard Held's new line of javelins raised interest and curiosity to the extent that starting in 1968, at the University of Maryland and the U.S. Department of the Army Ballistic-Transonic Laboratories, at the Aberdeen, Juris Terauds conducted and directed extensive aerodynamic and ballistic tests on competition javelins. The tests were conducted in wind tunnels and transonic ranges, and the javelins were propelled with javelin launchers and javelin guns. The end reports in 1971 provided new research data and understanding of the dramatic influence of air during the javelin's flight. Using this new knowledge Juris Terauds and Richard Held took the javelin design to the limits of the International Association of Athletic Federations (IAAF) rules, and Richard Held manufactured aerodynamically improved javelins which set all new world records. From this we now know that to achieve flight distance the aerodynamic and ballistic characteristics of the javelin play a major role. At the time, the new, long javelin flights, over one hundred meters, with the “aerodynamic” javelins started to get too long for existing stadiums. Consequently, with spectator safety in mind the IAAF set out to decrease the new long flight distances by tightening the javelin specification rules. In particular, the javelin's center of gravity was moved forward so that the center of pressure on all javelins is always behind the javelin's center of gravity, always creates a negative pitching moment and always causes the javelin to fly without a significant angle of attack.

Today the javelin manufacturers are following the new IAAF rules and producing javelins without taking advantage of the possibilities presented by new available materials. With the new available materials the javelin can be transformed, by completely changing its transverse moment of inertia and thereby improving its flight. However, the significance of the Javelin's transverse moment of inertia, which is not regulated by the IAAF rules, has been overlooked.

The mentioned official IAAF rules, which govern all javelin competitions, including the Olympic Games, define the size and shape of the javelins at all weights. However, for the sake of clarity, we will refer to the men's 800 gram javelin only, although the new art applies to all javelins. The specifications of the 800 gram javelin are: the overall length is 260.0 to 270.0 centimeters (cm), the distance front the front tip to the center of gravity is 90.0 to 106.0 centimeters., distance from the end of the tail to the center of gravity is 154.0 to 180.0 centimeters, the length of the metal head is 25.0 to 33.0 centimeters, the length of the cord grip is 15.0 to 16.0 centimeters, the maximum diameter of the shaft at the grip is 25 to 30 millimeters (mm), the maximum diameter 15.0 centimeters from the front tip is 80% of that javelin's maximum diameter, the maximum diameter half way from the front tip to the center of gravity is 90% of that javelin's maximum diameter, the minimum diameter half way from the end of the tail to the center of gravity is 90% of that javelin's maximum diameter, the minimum diameter 15.0 centimeters from the end of the tail is 40% of that javelin's maximum diameter, the minimum diameter of the tail end is 3.5 mm., and the maximum diameter of the cord grip is 8.0 mm greater than the maximum diameter of that javelin's shaft.

As mentioned, on all javelins, within the IAAF rules, the air center of pressure during flight remains behind the javelin's center of gravity, creating a negative pitching moment and forcing the javelin to fly without a significantly beneficial angle of attack. However, this negative pitching moment about said transverse axis is resisted by the javelin's transverse moment of inertia, which is not restricted by the rules. Research has shown that a javelin with an increased transverse moment of inertia is influenced less by the same pitching moment. This means that by manipulating the moment of inertia the influence of the pitching moment can be influenced. For example an adequately large moment of inertia prevents the pitching moment from rotating the javelin quickly enough about the transverse axis to eliminate a favorable angle of attack. The greater transverse moment of inertia forces the direction of the long axis of the javelin to lag behind the direction of the path of the javelin's center of gravity, thereby creating a positive angle of attack and with it a beneficial lift on the javelin.

The objective of the new art, is to provide an improved athletic competition javelin with better flight characteristics, so that increased distance can be achieved by the athlete.

BRIEF SUMMARY OF THE INVENTION

The present invention discloses a sports competition javelin designed to fly further. With the new art, the transverse moment of inertia of the javelin about the short axis, going through the javelin's center of gravity, is increased to the maximum. The javelin's mass is shifted as far as possible to the ends of the javelin, as far as possible away from the javelin's center of gravity, and away from the midsection under the cord grip. This placement of the mass at the ends of the javelin is limited only by the tensile strength of the latest available lightweight materials used for its construction. Also, with the availability of stronger materials in the future even more mass can be moved from the central part to the ends of the javelin, further increasing its transverse moment of inertia.

Up to the present, it has not occurred to the manufacturers of the old art that with new light materials the mass of the javelin can be moved and concentrated at the javelin's ends, increasing the javelin's transverse moment of inertia dramatically. As an example with the old, present art 800.0 gram javelins, the transverse moment of inertia ranges from 3314.0 to 4443.0 kilogram centimeters squared. By moving 400.0 grams of mass from the midsection of the javelin to the ends of the javelin the transverse moment of inertia is roughly doubled to 8000.0 kilogram centimeters squared. With this dramatic increase in the javelin's moment of inertia the influence of the negative pitching moment is diminished. This creates a situation where it takes significant time for the pitching moment to overcome the greater moment of inertia to rotate the javelin about its short axis. Consequently, an angle develops between the direction of the long axis of the javelin and the direction of the javelin's center of gravity. The angle that develops between the direction of the long axis of the javelin and the flight direction of the javelin's center of gravity is the angle of attack. In aerodynamics we know that it is crucial to have a positive angle of attack for creating lift. The beneficial lift continues on the javelin as long as there is a positive angle of attack, and there is a positive angle of attack as long as the direction of the long axis of the javelin has not caught up with the direction of the javelin's center of gravity. The time that the javelin spends flying through the air is only a few seconds. In this short time span, the direction of the long axis of the javelin never catches up with the direction of the javelin's center of gravity and consequently the javelin flies the full distance with an angle of attack, and a lift from the air below. In fact, within the limited flight time available the angle of attack can increase, making lift more significant.

This javelin flight phenomenon can further be explained in detail as follows: A javelin has a well defined, theoretical trajectory when it is launched and travels through air, just like other elongated projectiles. During the throw, just before the release the thrower applies the force along the long axis of the javelin at a desired angle of release. At the instant of release gravity starts to accelerate the javelin down, creating a positive angle of attack between the path of its center of gravity and the long axis of the javelin. When flying through the air with a positive angle of attack the javelin receives a lifting force from the air. The center of this lifting force on the javelin, called the center of pressure, is behind the center of gravity on the tail end of the javelin. With the center of pressure behind the javelin's center of gravity a negative pitching moment is developed, which tends to rotate the javelin about its center of gravity in a negative direction. The pitching moment is resisted by the javelin's transverse moment of inertia. The lower the javelin's transverse moment of inertia the greater the influence of the pitching moment on the direction of the long axis of the javelin. On the other hand a javelin's long axis direction, is influenced less by the same pitching moment when the transverse moment of inertia of that javelin is greater.

In other words the javelin with a low transverse moment of inertia is more sensitive to the pitching moment than a javelin with a high transverse moment of inertia. This also means that a javelin with a higher transverse moment of inertia will have a greater angular momentum at any angular velocity.

It is true, in every case, that the long axis position of a javelin with a higher transverse moment of inertia will be influenced less by a pitching moment of a given magnitude than a javein with a lower transverse moment of inertia. Under the present IAAF rules for the men's 800 gram javelin increasing the javelin's transverse moment of inertia to the maximum possible is beneficial for increasing flight distance.

It is an object of this invention to provide an athletic competition javelin design which will fly a greater distance.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The basic concept of the present invention takes into consideration all aspects of the old art, using the rule restrictions and specifications by the International Association of Athletic Federations (IAAF). The new art javelin consists of a head, a shaft and a cord grip attached to each other in a manner that satisfies the rules. The shaft is hollow, best described as a smooth tube, tapering toward both ends made from material which has the best practical strength weight ratio. The wall thickness of the shaft is made as thin and a light as possible, determined by the available material, with the required mass fixed in the very tail end. The metal head shape is machined according to the specifications of the rules with the proper mass, and it is machined such that it fits readily on the front of the shaft and is fixed to it. The cord grip is properly wound around the shaft, covering the javelin's center of gravity of the shaft, head and grip combined, and fixed to the shaft with adhesive material. The three mentioned javelin parts are made such that, when assembled, their combined mass is 800.0 grams, with their center of gravity 106.0 centimeters from the front tip.

The shaft is made of carbon fiber material, using appropriate epoxy resin and epoxy hardener to set the proper shape, by the mandrill machined for that purpose. The mandrill is machined such that the resulting 240.0 centimeter long carbon shaft is round and tapering, with a wall thickness of 0.75 mm, and a mass of 236.0 grams. A metal mass of 194.0 grams is formed to fit precisely in the very end of the shaft's tail, so that the combined mass makes one part with a weight of 430.0 grams. The head is machined from steel so that it is 33.0 centimeters long and has a mass of 336.0 grams, solid at the point end and tubular at the shaft-receiving end. The cord grip has a mass of 34.0 grams. The three parts make the total javelin mass 800.0 grams.

The above mentioned three parts make up the new art javelin with the following exterior dimensions: The overall length is 260.0 centimeters. The maximum diameter of the shaft is 30.0 mm, 105.0 centimeters from the front point. Going toward the point the diameter of the shaft is decreased the least amount possible, but enough so that a smooth convex shaft surface leads to a shaft diameter of 27.0 mm, 57.0 centimeters from the point, from there the diameter of the shaft continues to decrease in the same manner, until it reaches 25.0 mm, 33.0 centimeters from the tip. This is the point at which the shaft enters the cavity of the head. The diameter of the head 33.0 centimeters from the point is 27.5 mm, decreasing in diameter gradually, to reach 24.0 mm 15.0 centimeters from the point. Continuing toward the point, the diameter of the head is decreased gradually to 19.0 mm, 3.0 centimeters from the point. From there the decrease of diameter is abrupt, so that the diameter decreases 19.0 mm over 3.0 centimeters to a point.

The diameter of the shaft from the center of mass toward the tail of the javelin is decreased as much as possible, so that the diameter immediately after the cord grip, 15.0 centimeters from the center of gravity is 29.75 mm. From here the diameter of the shaft is decreased in a straight line so that 77.0 centimeters from the center of mass it is 27.0 mm, then the diameter continues to decrease so that 15.0 centimeters from the tip of the tail the shaft diameter is 12.0 mm. From 15.0 centimeters from the tail to the very end of the tail the diameter decreases in a straight line to 3.5 mm, which is the maximum tail diameter allowed.

The cord grip on the shaft has a diameter of 38.0 mm, or 8.0 mm greater than the shaft and is secured to the shaft, covering the shaft from 105.0 to 121.0 centimeters from the front tip.

At a transverse moment of inertia of roughly 8000 kilogram centimeters squared, the new art javelin, described above, has a dramatic increase in its transverse moment of inertia, when compared with the old art javelins with transverse moments of inertia around 4000 kilogram centimeters square. With roughly twice the transverse moment of inertia the new art javelin will fly significantly longer distances because of the resulting improved angle of attack, and therefore lift.

The transfer of mass from the central part of the javelin shaft to its ends can be carried out in several known ways, all of which result in transverse moment of inertia increases. The method of achieving the mass transfer to the javelin ends is of no consequence and is not at issue. The only issue is that the mass is moved to the ends of the javelin and that the transverse moment of inertia of the javelin is increased. In like manner, the material used to achieve the new art is not at issue. There can be numerous materials or combinations of materials involved in achieving the lightest possible javelin shaft with the greatest possible mass at the ends, to create the greatest possible transverse moment of inertia.

To test the new art, a new art competition javelin was constructed with the measurements as specified above, with the mass concentrated at both ends of the javelin, resulting in a javelin with a moment of inertia of 7980.0 kilogram centimeters squared. This new art javelin was matched up with a high quality carbon tube old art javelin, with a moment of inertia of 3981.0 kilogram centimeters squared.

Both javelins were thrown in sets, repeatedly, by the same throwers, with the flight distances measured. The results show that in the range between 60.0 and 65.0 meters for the old art javelin, the new art javelin flew 3.76 meters further and that in the range between 65.0 and 70.0 meters for the old art javelin the new art javelin flew 4.07 meters further. From this it was concluded that there was merit in the new art competition javelin with the benefit increasing with distance. 

I claim:
 1. A competition javelin, conforming to javelin competition regulations, comprising a tubular elongated body having a pointed front end and a tail end, with a grip over its center of gravity, with the mass of the javelin distributed such that the maximum transverse moment of inertia about its center of gravity is obtained.
 2. The competition javelin as defined in claim 1 wherein the javelin mass of suitable material is concentrated at both ends of the javelin.
 3. The competition javelin as defined in claim 1 wherein the tubular body of adequate strength is made of the lightest material practical. 